WNv FAQ

Find answers to common questions about West Nile virus in Alberta and its relationship to wildlife and human health.

Frequently Asked Questions about West Nile Virus

Dead Bird Handling and Testing

What do I do if I find a dead bird?

If you find a dead bird, you can:

  • Leave it alone
  • Bury it
  • Wrap the bird in plastic and put it out with the garbage (in urban areas)

When dealing with any "found dead" wildlife:

  • Always wear gloves.
  • Use a double plastic bag inverted over your hand, or use a stick to move the dead animal into a container.
  • Do not handle found dead wildlife directly with your hands.

As in previous years, outbreak situations involving clusters of dead birds found in a small area and over a short time frame should be reported to a Fish and Wildlife office. While not likely to be West Nile virus, the cause of the mortality may be some other disease occurrence that should be investigated.

To find the Fish and Wildlife office closest to you, see:

Can I still submit a dead bird for virus testing?

The province of Alberta does not conduct West Nile virus surveillance of individual wild birds: the program was discontinued in 2007.

The surveillance program was originally designed to provide an early warning system to alert the public and officials to the presence of the West Nile virus. Since its arrival in Alberta in 2003 the virus has exhibited a consistent pattern of occurrence. It returns each summer in July and August, and only in southeastern Alberta.

The extent of the affected area varies slightly depending on local weather patterns and associated populations of Culex tarsalis, the only mosquito involved in significant transmission of the virus in Alberta. In light of the predictability of the patterns, there is no need to submit individual dead birds for virus testing.

Why is Alberta no longer testing wild birds for West Nile virus?

When West Nile virus arrived in Alberta in 2003 it was entirely new to the province. Local bird populations had not been previously exposed and they had no natural immunity or resistance to infection. Members of the crow family (Corvidae: crows, magpies, jays, and ravens) were particularly susceptible and many died as a result of infection. These dead birds became an early warning system to show where and when the virus was active in the province. Health professionals, veterinarians, and the public used the information to assess the risk of possible infection.

Since 2003, we learned a lot about West Nile virus in Alberta:

  • We now know that suitable conditions for the virus are limited largely to the Grassland Natural Region of southeastern Alberta where conditions are most favourable for development of Culex tarsalis, the only mosquito that effectively transmits the virus in Alberta.
  • In addition, the number of dead corvids each summer declined significantly since the virus first appeared. Yet the populations of crows and magpies did not decline. It is likely that crows and magpies, as well as all the other birds species exposed to the virus, adapted to the presence of West Nile virus in the ecosystem and developed protective immunity. Thus monitoring dead birds no longer provides new information about West Nile virus.

We can safely predict that West Nile virus will reappear each year in July and August in southeastern Alberta. To avoid infection, people should continue to take appropriate measures to avoid being bitten by mosquitoes. Similarly, horse owners should provide appropriate protection against West Nile virus.

Virus Spread

Why didn't someone stop the spread of this virus?

Like any living organism, West Nile virus is well adapted for its own survival. It can survive in many species of birds and can use a wide range of mosquito species as a means of transferring the virus to new individuals.

From its arrival in North America on the east coast in 1999, it quickly spread among local bird populations. Many infected birds were migratory and carried the virus to southern climates where viral transmission continued as these birds intermingled with local mosquitoes and overwintering birds of the same or many different species.

During spring migration, the virus was carried northward in a variety of infected birds that spread out across the continent. Thus in 1999, the virus was restricted to the northeast U.S. By the end of 2001, it was in most states east of the Mississippi River as well as in southern Ontario. By the end of 2004, it was found in most provinces and states.

This expansion of the West Nile virus distribution reflects the primary bird migration pathways as the virus sequentially entered the Atlantic, Mississippi, Central, and Pacific Flyways. The virus continued to spread across North America and now occurs throughout Canada (except British Columbia and the maritime provinces), the continental United States, Mexico, Central America, and South America.

Risk Factors and Precautions

Are all birds susceptible?

Birds are the natural habitat for West Nile virus. It is likely that all bird species are susceptible to infection. To date, the virus has been identified in over 225 species of wild and captive bird species in North America. In addition, the virus can occasionally spill over into a few species of mammals and reptiles.

The U.S. National Wildlife Health Center is investigating the possibility that some North American raptor species, including some owl and hawk species common in Alberta, may be more susceptible to West Nile virus than most bird species. To date, there is insufficient information to allow any conclusions about the risk to these species.

Infection does not necessarily cause illness and the large majority of infected birds do not show any ill effects of having West Nile virus. Crows and their relatives are the exception. In these species the virus can cause illness and death in many individual birds.

Are wild mammals at risk?

Mammals in general are very resistant to infection with West Nile virus. Although individual wild mammals may be bitten by infected mosquitoes, they generally produce an immune response that prevents infection.

Thus, if we take a blood sample, we can find antibodies in various mammals but there is no virus present that could be passed on to mosquitoes. Of course, as with any infective agent, some individuals may not develop immunity and could become sick or perhaps even die.

Horses are an exception to the general rule for mammals and they are more susceptible to West Nile virus and closely related viruses. For good information about West Nile in horses, visit the Alberta Agriculture and Rural Development website at:

Do bird feeders pose a risk to birds or to humans?

Similar to the comments about handling live birds, bird feeders do not pose a significant concern either for the transmission of West Nile virus nor for the infection of humans. It is recommended that you change the water in bird baths regularly and drain stagnant water in your backyard to reduce mosquito breeding.

There have been ongoing problems with salmonella infections at bird feeders and as a result, feeders and birdbaths should be disinfected regularly with weak bleach. Since salmonella bacteria can infect humans, anyone handling potentially contaminated materials should wear gloves and wash thoroughly when the job is done. For more information, see the Avian Salmonellosis Fact Sheet at:

Should waterfowl hunters take special precautions?

Hunters, like all outdoor recreationists, should take precautions against being bitten by mosquitoes, which are common in wetland habitats and are active at dawn and dusk when temperatures are suitable for insect activity. Health officials advise that there is no evidence or reason to believe that there is any West Nile virus risk from handling hunter-killed birds in Alberta. Free-flying waterfowl are undoubtedly healthy; if not, they would be unable to fly.

In addition, the only In addition, the only evidence of direct transfer of West Nile virus from birds to humans without going through a mosquito involve accidental infection when lab technicians were handling many, many heavily infected birds.

Should bird banders take special precautions?

Health officials advise that there is no evidence of West Nile virus risk to persons handling live passerines (perching birds) or waterfowl in Alberta. The majority of birds are not infected and those that are do not contain significant numbers of virus and do not pose a threat to human health. Anyone handling live bAnyone handling live birds can always increase their protection by wearing gloves. Similar to hunting, bird banding activities often occur at dawn and dusk, thus banders should take precautions to avoid being bitten by mosquitoes.

Should bird rehabilitation facilities take special precautions?

There are growing concerns that captive or recuperating birds may be at increased risk of West Nile infection. Since it is likely that the virus will establish local populations in Alberta each summer, facility operators in the southern regions of the province would be well advised to screen the facility or take other precautions to avoid exposure of birds to mosquitoes. Preliminary investigation of a vaccine for birds looks somewhat promising, but is not available at this time. Although some facilities have used the horse vaccine on individual birds of critically endangered species, there is no evidence that it provides any protection to birds.

 

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Updated: Jun 16, 2015